Solibri Desktop (Solibri Office or Site) license or subscription doesn’t include the use of Solibri Inside Premium Subscription. This means that you can’t use the paid features of Solibri Inside.
You can use Solibri Inside with your existing Solibri Desktop credentials. You don’t need to create a new accout, just login with your Solibri username and password. After accepting the terms of service (for Solibri Inside), you have access to the free content. Using the paid content requires purchase.